Zirconium hydroxide supported metal and heteropolyacid catalysts

ABSTRACT

The present invention is directed to novel catalyst compositions, their preparation, and their use in a selective paraffin isomerization process. The solid acid catalyst compositions comprise a zirconium hydroxide support, a Group VIII metal, and a heteropolyacid selected from the group consisting of the exchanged aluminum salt of 12-tungstophosphoric acid, the exchanged salt of 12-tungstosilicic acid, and mixtures thereof. The use of said catalysts in an isomerization process comprises contacting said catalysts with a feed comprising C n  or C n  + paraffins, wherein n=4.

BACKGROUND OF THE INVENTION

The increasing emphasis on obtaining high octane non-aromatic fuelmolecules has increased the search for environmentally compatible solidacid catalysts, primarily oxides, for use in such processes as paraffinisomerization and alkylation. In the area of paraffin isomerization, thesolid acid catalyst should provide good activity at low temperaturesince thermodynamic equilibrium generally favors multibranched isomers,with high octane value, at lower temperature. In addition to maximizingproduct branching it is important to limit the amount of competingreactions, predominantly cracking, during isomerization. These crackingreactions are particularly problematic for acyclic paraffin feedmolecules C₇ + or larger.

The most commonly used catalysts in n-paraffin (C₅ and C₆) isomerizationinclude Pt supported on zeolites such as mordenite, or on highlychlorided aluminas which in the presence of continuous chlorine additionto the feed exist as aluminum trichloride supported on alumina. What isneeded in the art is an oxide based catalyst that can isomerizen-paraffins at low temperatures and in particular form very littlecracked products with C₇ + feeds. Furthermore, such catalysts wouldalleviate the environmental concerns associated with the inconvenient,environmentally detrimental chlorine addition required during operatingaluminum chloride based isomerization catalysts.

SUMMARY OF THE INVENTION

The supported heteropolyacid catalysts of the present invention catalyzethe isomerization of n-paraffins, such as heptane, at temperaturescomparable to those found using Pt-containing acidic zeolites such asmordenite or using strong acids based on or related to sulfated zirconia(ZrO₂ /SO₄). Unexpectedly, the amount of cracking of C₇ + paraffins issubstantially reduced.

The present invention is directed to novel catalyst compositions, theirpreparation, and their use in a selective paraffin isomerizationprocess. The present invention is directed to novel solid acid catalystcompositions comprising a zirconium hydroxide support, a Group VIIImetal, and a heteropolyacid selected from the group consisting of theexchanged aluminum salt of 12-tungstophosphoric acid, the exchanged saltof 12-tungstosilicic acid, and mixtures thereof. The use of saidcatalysts in an isomerization process comprises contacting saidcatalysts with a feed comprising C_(n) or C_(n) + paraffins, whereinn=4.

The process of making such catalysts comprises the steps of:

(a) impregnating a heteropolyacid selected from the group consisting ofthe exchanged aluminum salt of 12-tungstophosphoric acid, the exchangedaluminum salt of 12-tungstosilicic acid, and mixtures thereof onto azirconium hydroxide support;

(b) impregnating Group VIII metal onto said support before, during orsubsequent to step (a);

(c) activating said impregnated zirconium hydroxide support prior to andfollowing said impregnation step (b) if said Group VIII metal isimpregnated subsequent to step (a) or activating said impregnatedsupport after said impregnation of a heteropolyacid if said Group VIIImetal is impregnated before or during step (a) to form a catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the % conversion of n-heptane vs. temperature for fourcatalysts supported on zirconium hydroxide. Catalysts A and B areexchanged aluminum 12-tungstophosphoric acid and platinum with theplatinum precursor being either tetrammine platinum hydroxide orchloroplatinic acid, respectively. Catalysts C and D are12-tungstophosphoric acid and platinum with the platinum precursor beingeither tetrammine platinum hydroxide or chloroplatinic acid,respectively. The figure shows that on a Zr(OH)₄ support, the exchangedaluminum salt of 12-tungstophosphoric acid (i.e., Al.sub..83 H.sub..5PW₁₂ O₄₀) is more active than the 12-tungstophosphoric acid (H₃ PW₁₂ O₄₀·6H₂ O). The aluminum 12-tungstophosphoric acid and platinum catalystsshow low temperature (210°-270° C.) activity for C₇ isomerization,whereas the 12-tungstophosphoric acid and platinum catalysts do not.

FIG. 2 again compares catalysts A and B to typical prior art catalysts Eand F. Catalysts E (solid line) and F (line with boxes) are tungstenoxide supported on zirconium hydroxide containing aluminum and platinumwith the platinum precursor being either platinum tetrammine hydroxideor chloroplatinic acid, respectively. Catalysts E and F containingtungsten oxide and alumina in place of the exchanged aluminum12-tungstophosphoric acid are not active.

FIG. 3 shows that catalysts A and B exhibit less cracking than a typicalprior art platinum containing sulfated zirconia catalyst (diagonal bar)(see U.S. Pat. No. 5,120,898) when run at comparable conversions.Similar conversions were obtained by operating catalysts A and B at 240°C. while the sulfated zirconia catalyst was run at 180° C.

FIG. 4 shows the % conversion of n-heptane vs. temperature in ° C. forcatalysts G, H, I, J, K and L which are analogous to catalysts A, B, C,D, E, and F except that the support is silica instead of zirconiumhydroxide and no aluminum is added to catalysts K and L. The12-tungstophosphoric acid and platinum incorporated via chloroplatinicacid (J) and the exchanged aluminum 12-tungstophosphoric acid andplatinum incorporated via chloroplatinic acid (H) show low temperatureactivity. The aluminum did not affect catalyst activity of12-tungstophosphoric acid and the tungsten oxide (ammonium metatungstateprecursor) based catalysts are inactive as is catalyst G having platinumincorporated via platinum tetrammine hydroxide.

FIG. 5 shows the conversion of n-heptane, % selectivity to crackedproducts (C₆ -), dimethyl pentanes, and methyl hexanes for catalysts Hand J.

Catalyst Designation of Figures

A: Pt/Al.sub..83 H.sub..5 PW₁₂ O₄₀ /Zr(OH)₄ *

B: Pt/Al.sub..83 H.sub..5 PW₁₂ O₄₀ /Zr(OH)₄ **

C: Pt/H₃ PW₁₂ O₄₀ /Zr(OH)₄ *

D: Pt/H₃ PW₁₂ O₄₀ /Zr(OH)₄ **

E: Pt/WO₃ (&Al)/Zr(OH)₄ *

F: Pt/WO₃ (&Al)/Zr(OH)₄ **

G: Pt/Al.sub..83 H.sub..5 PW₁₂ O₄₀ /SiO₂ *

H: Pt/Al.sub..83 H.sub..5 PW₁₂ O₄₀ /SiO₂ **

I: Pt/H₃ PW₁₂ O₄₀ /SiO₂ *

J: Pt/H₃ PW₁₂ O₄₀ /SiO₂ **

K: Pt/WO₃ /SiO₂ *

L: Pt/WO₃ /SiO₂ **

* 0.3 wt. % platinum incorporated using tetrammine platinum hydroxide

** 0.3 wt. % platinum incorporated using chloroplatinic acid

DETAILED DESCRIPTION OF THE INVENTION

Heteropoly acids form by condensation of two or more oxyacids, e.g.,phosphoric or silicic acid with tungstic acid, and contain largepolyoxometallate anions with interstitial hydrated protons and variablelevels of water of hydration. The heteropolyacids are soluble in wateror polar oxygenated hydrocarbons, such as alcohols or ethers. Theparticular heteropoly acids of the present catalysts are acids withanions adopting the well known Keggin structure and are represented byformulas: H₃ PW₁₂ O₄₀ ·6H₂ O (phosphotungstic acid or12-tungstophosphoric acid), and H₄ SiW₁₂ O₄₀ ·6H₂ O (12-tungstosilicicacid or silicotungstic acid). They contain a central tetrahedral PO₄ orSiO₄ group connected to 12 surrounding WO₃ octahedra and can beconsidered the condensation product of phosphoric or silicic acid withtungstic acid.

These water soluble acids can be deposited on supports by impregnationtechniques well known to those skilled in the art such as by anincipient wetness technique.

The supports of the instant invention, silica when the heteropoly acidis 12-tungstophosphoric acid, 12-tungstosilicic acid, the exchangedaluminum salt of 12-tungstophosphoric acid, and the exchanged aluminumsalt of 12-tungstosilicic acid, and zirconium hydroxide when theheteropoly acid is the exchanged aluminum salts of 12-tungstophosphoricacid and 12-tungstosilicic acid are commercially available or may beprepared by well known techniques. For example, the zirconium hydroxidemay be precipitated, at a pH of 9, from a solution of zirconyl chlorideand ammonium hydroxide followed by washing to remove residual chlorideions. Preferably the supports will be thermally treated prior to use.Preferably the silica will be calcined at about 500° C. and thezirconium hydroxide at about 110° C. Partially exchanged as used hereinmeans that Al⁺³ is substituted into the heteropolyacid to replace some,but not all, of the protons. The amount of exchange depends upon theamount of aluminum utilized and is readily determinable by one skilledin the art. Preferably between 0.5 and 2.75 of the protons are exchangedwith Al⁺³ cations, more preferably between 2.25 and 2.5 will beexchanged. It is obvious to one skilled in the art that all of theprotons cannot be exchanged or acidity will be lost. For example

    H.sub.3 PW.sub.12 O.sub.40 ·6H.sub.2 O=(H.sub.5 O.sub.2).sub.3.sup.+ PW.sub.12 O.sub.40

is exchanged to

    Al.sub.5/6 (H.sub.5 O.sub.2).sub.1/2.sup.+ PW.sub.12 O.sub.40

in which 2.5 of the 3 hydrated protons have been replaced.

The heteropoly acid (HPA) and Group VIII metal may be coimpregnated ontothe support, the Group VIII metal impregnated first, or the Group VIIImetal can be impregnated supsequent to the HPA. Preferably, however, theHPA is impregnated first followed by impregnation of the Group VIIImetal.

The Group VIII metal can be impregnated onto the support by any of thetechniques known to those skilled in the art. For example, the incipientwetness technique, or an absorption technique from a dilute orconcentrated solution, with subsequent filtration or evaporation toeffect uptake of the metallic Group VIII component. The impregnation canbe carried out under a variety of conditions known to those skilled inthe art, including ambient and elevated temperatures, and atmosphericand superatmospheric conditions.

The amount of Group VIII metal will range from about 0.01 to about 10wt. %, preferably about 0.2 to about 1.0 wt. %, and most preferablyabout 0.3 to about 0.7 wt. %.

The amount of heteropolyacid to be impregnated onto the support willrange from about 0.01 to about 60 wt. %, preferably about 10 to about 50wt. %, and most preferably about 25 to about 40 wt. %.

Once the heteropolyacid is impregnated onto the support, the support isdried at about 100° to about 120° C. for at least 4 hours followed bycalcination at about 250° to about 500° C., preferably 300° C. for atleast 4 hours. This drying and calcination is herein referred to asactivation. If coimpregnation is used, only one drying and calcinationunder the above conditions will be carried out. If the Group VIII metalis impregnated prior to the HPA, only the drying step will be carriedout and activation will be conducted following the HPA impregnation. Ifthe HPA is impregnated first followed by the Group VIII metal,activation will occur before and after the impregnation of the GroupVIII metal. If the HPA and Group VIII metal are coimpregnated,activation will occur following coimpregnation.

The Group VIII metals useable for the present invention catalysts areany of the Group VIII metals of the periodic table, namely iron, cobalt,nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum andmixtures thereof. Preferably a Group VIII noble metal will be employed,most preferably platinum.

Applicants have found that the platinum metal precursor has littleeffect on catalyst activity for 12-tungstophosphoric acid or theexchanged aluminum salt of 12-tungstophosphoric acid when the support iszirconium hydroxide. However, the platinum metal precursor becomes animportant parameter with respect to catalyst selectivity. Applicantshave found that with a zirconium hydroxide support the exchangedaluminum 12-tungstophosphoric acid with platinum incorporated by use ofa tetrammine platinum hydroxide precursor, dramatically reduces theselectivity to cracked products compared to one prepared withchloroplatinic acid as the precursor. Additionally, applicants havefound that although the addition of aluminum to 12-tungstophosphoricacid on silica is not critical, the platinum precursor is. Only thosecatalysts made with chloroplatinic acid are active; platinum tetramminehydroxide produces inferior catalysts. The examples will make thisreadily evident. Hence, when preparing a catalyst comprising thealuminum salt of 12-tungstophosphoric acid and Group VIII metal on azirconium hydroxide support, it is preferable that the Group VIII metalprecursor be present in a cationic form; the resulting isomerizationreaction is accompanied by less cracking side reactions. However, theGroup VIII precursor can also be added as an anionic complex in whichcase activity will be comparable but the increased selectivity will notbe afforded. When preparing a catalyst comprising 12-tungstophosphoricacid and Group VIII metal on silica, the Group VIII metal precursor mustbe present as an anionic complex. Any Group VIII metal precursorsmeeting this criteria are acceptable for use.

Cationic form means the Group VIII metal is present as a cation, e.g.,tetrammine platinum hydroxide, tetrammine platinum chloride, anddinitrodiammineplatinum (II), or any other cationic forms of Group VIIIcompounds known to those skilled in the art can be used. Anioniccomplexes means the Group VIII metal is contained in an anionic complexsuch as e.g. (PtCl₄)⁻² wherein the complex is negatively charged.Examples of suitable anionic complexes are chloroplatinic acid (known ashydrogen hexachloroplatinate (IV)), ammonium tetrachloroplatinate (II),ammonium hexachloroplatinate (IV), bromoplatinic acid (known as hydrogenhexabromoplatinate (IV)), and chloroiridic acid. The above lists ofcompounds containing Group VIII metals as cations or in anioniccomplexes are merely illustrative and not meant to be limiting.

The catalysts of the present invention are useful in an isomerizationreaction. The isomerization reaction is carried out at temperatures ator below about 500° C., preferably 25°-250° C.; 15 to 3000 psi H₂,preferably 100 to 1500 psi H₂ ; 1 to 100, preferably 2 to 12.0 WHSV; andH₂ /paraffin ratio of 1:1 to 10:1, preferably 3:1 to 7:1.

The exchanged aluminum salt of 12-tungstophosphoric acid and platinum onzirconium hydroxide exhibits low temperature activity for C₇isomerization. It exhibits increasing activity from about 220° C. toabout 300° C. and the selectivity to cracked products at 30% conversionis only 10%.

The 12-tungstophosphoric acid or the exchanged aluminum salt andplatinum supported on silica also exhibits low temperature activitybetween about 210° C. and 260° C. Hence, the catalysts of the presentinvention are particularly useful for low temperature isomerizationprocesses at temperatures where conventional (e.g. supported tungstenoxide) catalysts are inadequate.

The following examples are illustrative of the invention and are notmeant to be limiting.

EXAMPLES

A suite of catalysts was prepared that contained the equivalent of 40wt. % WO₃ using 12-tungstophosphoric acid, the exchanged aluminum saltof 12-tungstophosphoric acid (Al.sub..83 H.sub..5 PW₁₂ O₄₀ salt),ammonium metatungstate, and ammonium metatungstate with added aluminumcations. These precursors were impregnated onto γ-Al₂ O₃, SiO₂,amorphous SiO₂ -Al₂ O₃ and Zr(OH)₄. 0.3 wt. % Pt is added to thesesupported heteropoly acids by using both chloroplatinic acid (Pt presentas an anionic complex) or as tetrammine platinum hydroxide (Pt presentin a cationic form). In all cases the supported heteropoly acid orammonium metatungstate was calcined at 300° C. and the platinumprecursor was then decomposed at 300° C.

Example 1 Preparation of 12-Tungstophosphoric Acid

Dissolve 100 grams of sodium tungstate and 16 grams disodium phosphatein 1500 cc of water and heat to 80° to 90° C. for 30 minutes. To thisadd 80 cc of concentrated HCl dropwise. A precipitate forms after abouthalf of the HCl is added. After 30 minutes of stirring, add 60 cc ether,stir and shake. Three layers form. The lower layer is washed three timeswith water and enough ether is added to form three additional layers.This is repeated several times and finally the lower layer is dried byaspiration with air. Alternatively a commercial source of12-tungstophosphoric acid can be used, and it is first dried for 2 to 5hours at 110° C. In both cases, the product shows the characteristiccubic x-ray diffraction pattern spectrum characteristic of the Kegginstructure. See, e.g., G. M. Brown, M. R. Spirlet, W. R. Busing and H. A.Levy, Acta Cryst. B33, 1038-46 (1977).

Example 2 Preparation of 40% Phosphotungstic Acid (HPW) on Supports

Four different supports were used. A commercial supply of reforminggrade gamma alumina with a surface area of 180 m² /g, a commercialsupply of SiO₂ (350 m² /g), a commercial supply of an amorphous SiO₂-Al₂ O₃ (350 m² /g), and a laboratory prepared sample of Zr(OH)₄. Thefirst three commercially prepared supports were calcined at 500° C.prior to use. The Zr(OH)₄ was prepared by precipitating an aqueoussolution of zirconyl chloride with ammonium hydroxide to reach a pH of 9and washing the precipitate repeatedly with a pH 9 ammonium hydroxidesolution to remove residual chloride ions. This was then dried at 100°C. and used as support with (220 m² /g) surface area. In each case 31.8gm of the 12-tungstophosphoric acid hexa-hydrate was dissolved in enoughwater to impregnate by incipient wetness 45 grams of the above foursupports. These were then dried at 110° C. overnight and then calcinedat 300° C. in air for three hours.

Example 3 Preparation of 40% Aluminum-Phosphotungstic Acid (Al-HPW)(Al.sub..83 H.sub..5 PW₁₂ O₄₀) on Supports

The same four supports were used as in Example 2. 35.3 grams of12-tungstophosphoric acid and 3.59 g of aluminum nitrate nonahydratewere dissolved in sufficient water to impregnate by incipient wetness 50grams of each support. These were then dried at 110° C. overnight andthen calcined at 300° C. in air for three hours.

Example 4 Preparation of 40% WO₃ on Supports

The same four supports were used as in Examples 1 and 2. 21.6 grams of acommercially available ammonium metatungstate (92.3% WO₃) were dissolvedin sufficient water to impregnate by incipient wetness 30 grams of eachsupport. These were then dried at 110° C. overnight and then calcined at300° C. in air for three hours.

Example 5 Preparation of 40% WO₃ (with Al) on Supports

The same four supports were used as in Examples 1, 2, and 3. 21.6 gramsof a commercially available ammonium metatungstate (92.3% WO₃) and 2.16grams of aluminum nitrate nonahydrate were dissolved in sufficient waterto impregnate by incipient wetness 30 grams of each support. The Al:Wmolar ratio was the same as for the heteropolyacids of Example 2. Thesewere then dried at 110° C. overnight and calcined at 300° C. in air forthree hours.

Example 6 Properties and Initial Acidity Characterization of SupportedHeteropoly Acids and WO₃ Catalysts

Table 1 lists the acid strength parameters for the catalysts prepared inExamples 2-5 when run in the 2-methyl-2 pentene reaction test (2MP2),(reference test: Kramer and McVicker, Accounts of Chemical Research, 19,78 (1986)).

The formation rates and rate ratios of the product hexene isomers ofthis test reaction reflect the acid site concentration and strength ofthe catalyst respectively. The product hexene isomers formed include4-methylpent-2-ene (4MP2), t-3-methylpent-2-ene (t-3MP2), and 2,3dimethylbute-2-ene (2,3 DMB2). 4MP2 requires only a double bond shift, areaction occurring on weak acid sites. 3MP2 requires a methyl groupshift (i.e., stronger acidity than double bond shift), whereas 2,3DMB2requires even stronger acidity to produce a second methyl branch. For ahomologous series of solid acids, differences in t-3MP2 rates normalizedwith respect to surface area reflect the density of acid sitespossessing strengths sufficient to catalyze the skeletal isomerization.Since skeletal isomerization rates generally increase with increasingacid strength, the ratio of methyl group migration rate to double bondshift rate should increase with increasing acid strength. The use ofrate ratios, in lieu of individual conversion rates is preferable sincedifferences in acid site populations are normalized.

                                      TABLE 1                                     __________________________________________________________________________    SUMMARY OF SUPPORTED HETEROPOLY ACIDS                                         Precursor Effects                                                                                                    40% Aluminum Exchanged                                                                       40% WO.sub.3                                    40% 12-Tungstophosphoric                                                                     12-Tungstophosphoric                                                                         Ammonium                Rate Ratios at 250° C.                                                                  Support                                                                              Acid           Al.sub..83 H.sub..5 PW.sub.12                                                 O.sub.40       Metatungstate           1 Hr. On Stream  only   (300° C.)*                                                                            (300° C.)*                                                                            (300°            __________________________________________________________________________                                                          C.)*                    3MP2/4MP2; 2,3DMB2/4MP2                                                                        Zr(OH).sub.4                                                                         Zr(OH).sub.4   Zr(OH).sub.4   Zr(OH).sub.4                             n.a.   0.79; 0.066    2.12; 0.37     1.11; 0.094             3MP2/4MP2; 2,3DMB2/4MP2                                                                        SiO.sub.2                                                                            SiO.sub.2      SiO.sub.2      SiO.sub.2                                0.0; 0.0                                                                             1.75; 0.21     2.37; 0.54     0.59; 0.048             3MP2/4MP2; 2,3DMB2/4MP2                                                                        SiO.sub.2 -Al.sub.2 O.sub.3                                                          SiO.sub.2 -Al.sub.2 O.sub.3                                                                  SiO.sub.2 -Al.sub.2 O.sub.3                                                                  SiO.sub.2 -Al.sub.2                                                           O.sub.3                                  2.87; 0.69                                                                           2.44; 0.32     2.03; 0.23     2.08; 0.32              3MP2/4MP2        Al.sub.2 O.sub.3                                                                     Al.sub.2 O.sub.3                                                                             Al.sub.2 O.sub.3                                                                             Al.sub.2 O.sub.3                         0.04; 0.03                                                                           2.04; 0.27     1.93; 0.24     1.75;                   __________________________________________________________________________                                                          0.20                     * = calcination temperature                                                   n.a. = not available                                                          MP2 = trans 3methylpent-2-ene                                                 MP2 = cis and trans 4methylpent-2-ene                                         2,3DMB2 = 2,3dimethylbutene-2                                            

The results summarized in Table 1 clearly show 1) the use of12-tungstophosphoric acid instead of ammonium metatungstate increasesthe acidity of the silica catalyst dramatically and 2) the aluminumphosphotungstate salt on zirconia is more acidic than either12-tungstophosphoric acid or ammonia metatungstate on zirconia.

Example 7 Preparation of 0.3% Pt on Supported Catalysts byChloroplatinic Acid

9.97 grams of the supported 12-tungstophosphoric acid, exchangedaluminum 12-tungstophosphoric acid, tungsten oxide and tungsten oxideplus Al described in Examples 2-5 were impregnated with 2.10 cc of achloroplatinic acid solution containing 0.15 g of Pt per 1.00 cc andfurther diluted with water to reach the incipient wetness volume. Theseimpregnates were then dried at 110° C. overnight and then calcined at300° C. in air for three hours.

Example 8 Preparation of 0.3% Pt on Supported Catalyst by TetramminePlatinum Hydroxide

9.97 grams of the supported 12-tungstophosphoric acid, exchangedaluminum 12-tungstophosphoric acid salt, tungsten oxide, and tungstenoxide plus Al described in Examples 2-5 were impregnated by incipientwetness using 2.0 g of a Pt tetrammine hydroxide solution (1.47 wt. %Pt) diluted to the incipient wetness volume. These catalysts were thendried at 110° C. overnight and calcined at 300° C. in air for threehours.

Example 9

The catalysts were run in a fixed bed micro reactor equipped withon-line GC analysis under n-heptane isomerization conditions. Thecatalyst, together with a quartz powder diluent, was added to a 6 inchreactor bed. A thermocouple was inserted into the center of the bed. Thecatalysts were calcined at 300° C. immediately prior to use and reducedin H₂ at 200° C. for 1 hour. The feed was introduced via a liquid feedpump. The runs were made at 160 psi with a H₂ /n-heptane feed ratio of 7and a weight hourly space velocity of 11. For those runs where atemperature ramping profile was followed, the isomerization was run for4.5 hours during which three data points were collected and averaged.The temperature then increased 10 to 20 degrees and catalyst datameasured another four and a half hours. The results are shown in FIGS.2-6.

The catalysts of the FIGS. 1-5 and Example 9 are as follows:

Catalyst A is exchanged aluminum 12-tungstophosphoric acid with platinumsupported on zirconium hydroxide where the platinum was incorporatedusing the cationic precursor platinum tetrammine hydroxide as theprecursor as in Example 3 and 8. Catalyst B is the same as catalyst Aexcept the platinum precursor was chloroplatinic acid as in Examples 3and 7. Catalyst C is 12-tungstophosphoric acid and platinum supported onzirconium hydroxide where the platinum precursor was platinum tetramminehydroxide as in Examples 2 and 8. Catalyst D is the same as catalyst Cexcept that the platinum was incorporated using chloroplatinic acid asin Examples 2 and 7. Catalyst E is tungsten oxide with aluminum andplatinum on zirconium hydroxide where the platinum was incorporatedusing platinum tetrammine hydroxide as in Examples 5 and 8. Catalyst Fis the same catalyst as Catalyst E except that the platinum wasincorporated using chloroplatinic acid as in Examples 5 and 7. CatalystsG, H, I, J, K and L are catalysts on silica supports. Catalysts G and Hare exchanged aluminum 12-tungstophosphoric acid and platinum where theplatinum is incorporated via platinum tetrammine hydroxide andchloroplatinic acid respectively, Examples 3 and 8, and 3 and 7respectively. Catalyst I and J are 12-tungstophosphoric acid andplatinum where the platinum was incorporated via platinum tetramminehydroxide and chloroplatinic acid respectively, Examples 2 and 8 and 2and 7 respectively. Catalysts K and L are tungsten oxide and platinumwhere the platinum was incorporated via platinum tetrammine hydroxideand cholorplatinic acid, respectively, Examples 4 and 8 and 4 and 7respectively.

FIG. 1 shows that the Al-HPW is more effective than the pure HPW acidwhen impregnated onto Zr(OH)₄. The platinum precursor has little effecton the relative activity. FIGS. 1 and 2 show that either the plain HPWprecursor or the ammonium metatungstate (AMT) precursors with added (Al)do not form effective catalysts regardless of the platinum precursor.The Al-HPW precursor on zirconia however is active and shows increasingactivity with rising temperature from 220° to 300° C. FIG. 3 shows theinteresting selectivity behavior of Al-HPW on Zr(OH)₄ made with thetetrammine platinum hydroxide percursor. At comparable conversions to aZrO₂ /SO₄ catalyst as well as Al-HPW/Zr(OH)₄ made with chloroplatinicacid the selectivity to cracked products is dramatically diminished.This is quite important and unexpected.

FIG. 4 shows the behavior of the HPW and Al-HPW catalysts on SiO₂. Inthis case the addition of aluminum is not critical, but the platinumprecursor becomes the important parameter. Only those catalysts madewith chloroplatinic acid are active; platinum tetrammine hydroxideproduces inferior catalyst. The comparative example catalyst made withthe AMT percursor, i.e., WO₃ /SiO₂ and (WO₃ & Al)/SiO₂ are also notactive at all. FIG. 5 shows that the selectivity to cracking atcomparable conversions is lower on the HPW on SiO₂ catalyst than on theAl-HPW on SiO₂ catalyst.

What is claimed is:
 1. A solid acid catalyst composition comprising azirconium hydroxide support about 0.01 to about 10 wt. % of a Group VIIImetal and about 0.01 to about 60 wt. % of an exchanged heteropolyacidsalt selected from the group consisting of the exchanged aluminum acidsalt of 12-tungsto- phosphoric acid, the exchanged aluminum acid salt of12-tungstosilicic acid, and mixtures thereof.
 2. A catalyst compositionaccording to claim 1 wherein said Group VIII metal is selected from thegroup consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium,osmium, iridium, platinum, and mixtures thereof.
 3. A catalystcomposition according to claim 2 wherein said Group VIII metal is aGroup VIII noble metal.
 4. A catalyst composition according to claim 3wherein said Group VIII noble metal is platinum.
 5. A solid acidcatalyst composition according to claim 1, said heteropoly acid is theexchanged aluminum salt of 12-tungstophosphoric acid and said Group VIIImetal is platinum.
 6. A process of preparing a solid acid catalystcomprising a support, about 0.01 wt. % to about 10 wt. % of a Group VIIImetal, and about 0.01 to about 60 wt. % of an exchanged heteropolyacidsalt comprising the steps of(a) impregnating a heteropolyacid selectedfrom the group consisting of the exchanged aluminum acid salt of12-tungstophosphoric acid, the exchanged aluminum acid salt of12-tungstosilicic acid, and mixtures thereof onto a zirconium hydroxidesupport; (b) impregnating Group VIII metal onto said support before,during, or subsequent to step (a); (c) activating said impregnatedzirconium hydroxide support prior to and following said impregnationstep (b) if said Group VIII metal is impregnated subsequent to step (a)or activating said impregnated support after said impregnation of aheteropolyacid salt if said Group VIII metal is impregnated before orduring step (a) to form a catalyst.
 7. A process of preparing a solidacid catalyst according to claim 6 wherein said Group VIII metal isimpregnated via a solution selected from the group consisting ofchloroplatinic acid, ammonium tetrachloroplatinate (II), ammoniumhexachloroplatinate (IV), chloroiridic acid, tetrammine platinumhydroxide, tetrammine platinum chloride, and dinitrodiammineplatinum(II).